Future for CCA timber
Friday 9 Feb 2024
Every year, thousands of tonnes of CCA-treated timber are sent to secure landfills. There are currently limited disposal options for the timber, which has been treated with a mix of copper, chromium and arsenic.
One of the most widely used wood preservatives worldwide, chromated copper arsenate (CCA) enhances the durability of wood, meaning timber products are more resilient to decay and insect attack. It is commonly used in construction, landscape gardening and horticulture with hundreds of CCA- treated posts per hectare in vineyards.
But at the end of its life the wood has limited reuse value and, due to environmental challenges with the treatment components like arsenic, limited disposal options.
Incineration or pyrolysis is technically challenging. Most of it goes to secure landfills. Exactly how much is sent to landfill is hard to quantify because CCA makes up a portion of demolition waste which is often unsorted. A 2021 Ministry for the Environment report showed almost three million tonnes of class 2 to 5 waste is sent to landfill each year. Construction and demolition waste could be in classes 2-4 and contain CCA timber.
Scientists at Scion have been researching removing CCA from treated timber at the end of its life and separating it into individual elements.
Senior technologist Sean Taylor discovered there could be a way to remove CCA from the timber in 2015 and began research to find an efficient removal process. The early successes led to a $163,000 Waste Minimisation Fund grant to continue investigating the feasibility of remediating treated timber.
Taylor has made good progress removing CCA and recovering the copper and arsenic, but more work needs to be done recovering individual elements – particularly isolating a high enough percentage of chromium. “The issue became how can we get the metal components out and how can we isolate them individually?” Taylor says.
While a future use for the remediated timber and recovered elements would need to be determined by users, once successfully isolated, the elements could then be reused in things like electronics or compound metals, keeping them in the circular bioeconomy.
“If you’re just taking it out of the timber and putting it into a bucket, you’re just moving the problem around.”
Taylor says a solution to CCA timber is vital because putting it in the landfill or worse, burning it without suitable technology and infrastructure, is “not the wise or right thing to do long term”.
Scion’s Circular Manufacturing programme aims to show wood materials can go into circularity beyond burning … We can use new technology to solve hard and old challenges.”
Gaugler says Scion has shown there are end-of-use options for CCA-treated timber, but it needs to happen on a large scale. The question is who pays for resource recovery and waste management addressing the issue and adding value by eliminating a problem.
Source & image credit: Scion
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